IB/ipoib: Delete unused struct

This structure is not needed since the introduction of commit
'c4268778 ("IB/ipoib: Scatter-Gather support in connected mode")'

Signed-off-by: Yuval Shaia <yuval.shaia@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>